Marble as a _Speculum_, was but very Faint and
exceeding ill Defin'd. Secondly, That taking two pieces of Plain and
Polish'd Surfaces, and casting on them Successively the Beams of the Same
Candle, In such manner, as that the Neighbouring Superficies being Shaded
by an Opacous and Perforated Body, the Incident Beams were permitted to
pass but through a Round Hole of about Half an Inch Diameter, the Circle of
Light that appear'd on the White Marble was in Comparison very Bright, but
very ill Defin'd; whereas that on the Black Marble was far less Luminous,
but much more precisely Defin'd.

6. Thirdly, When you Look upon a piece of Linnen that has Small Holes in
it, those Holes appear very Black, and Men are often deceiv'd in taking
Holes for Spots of Ink; And Painters to represent Holes, make use of Black,
the Reason of which seems to be, that the Beams that fall on those Holes,
fall into them So Deep, that none of them is Reflected back to the Eye. And
in narrow Wells part of the Mouth seems Black, because the Incident Beams
are Reflected Downwards from one side to another, till they can no more
Rebound to the Eye.

We may consider too, that if Differing parts of the same piece of Black
Velvet be stroak'd Opposite ways, the piece of Velvet will appear of two
Distinct kinds of Blackness, the one far Darker than the other, of which
Disparity the Reason Seems to be, that in the Less obscure part of the
Velvet, the Little Silken Piles whereof 'tis made up, being Inclin'd, there
is a Greater part of each of them Obverted to the Eye, whereas in the other
part the Piles of Silk being more Erected, there are far Fewer Beams
Reflected Outwards from the Lateral parts of each Pile, So that most of
those that Rebound to the Eye, come from the Tops of the Piles, which make
but a small part of the whole Superficies, that may be cover'd by the piece
of Velvet. Which Explication I propose, not that I think the Blackness of
the Velvet proceeds from the Cause assign'd, since each Single Pile of Silk
is Black by reason of its Texture, in what Position soever you Look upon
it; But that the Greater Blackness of one of these Tuffts seems to proceed
from the Greater Paucity of Beams Reflected from it, and that from the
Fewness of those Parts of a Surface that Reflect Beams, and the Multitude
of those Shaded Parts that Reflect none. And I remember, that I have
oftentimes observ'd, that the Position of Particular Bodies far greater
than Piles of